Many Android phones come with very little storage, of which the operating system already consumes around 6GB. Fortunately, phones with Android 6.0 Marshmallow or later can expand their storage in a snap. But a few problems can make using expandable storage difficult.

Second, microSD cards need configuration. If you simply stick a card in a phone, it won’t necessarily move all your files over onto it. First-time use of a microSD card may require manually transferring apps and files.

Third, you can’t use a microSD card in a computer and smartphone. Android 6.0 Marshmallow (and newer) prevents users from swapping their card between computers and using it as external storage (unless you know a certain trick).

Fourth, creating a backup of microSD cards on Android 6.0 or newer is a pain. Unfortunately, no easy answer exists. In the short term, if you want to migrate from a smaller card to a larger one, you don’t have any good options in Android 6.0 or later.

1. Buy the Best microSD Card

Unless your phone includes a microSD card slot, you’re out of luck. However, if your phone is compatible and you want a microSD card, know the kind of card you need. Find two things: one, how large a microSD card your phone can handle and, two, the fastest card for your needs.

microSD Card Size and Speed

microSD cards fall into three capacity classifications. Two of these are still used on Android devices: Secure Digital High Capacity (SDHC), and Secure Digital eXtended Capacity (SDXC). SDHC covers cards under 32GB, and SDXC covers cards between 64GB and 128GB. In general, phones more than five years old probably use SDHC, while newer phones tend to use SDXC.

When picking a size, first find out the maximum size your phone can handle (that’s probably SDXC, or larger than 32GB) and estimate the amount of storage you need. Buy a capacity that is twice or 75 percent more than you need. A mostly filled card runs slower than an empty one.

After picking a card size, you need to choose a speed. The two most common certifications relevant to Android are UHS-I and Class 10. Some have argued that UHS-I is a faster standard than Class 10. When tested, though, the differences appear trivial:

For storing media files, the two standards are about equal in performance. However, if you plan on throwing apps on the card, look for a rating called app performance class, designated by an “A” rating followed by a conjoined number. Here’s a YouTube video explaining the certification:

A-Certification Is Deceiving and Uncommon

Unfortunately, the A1 standard is both deceiving and uncommon. What’s deceiving is that some cards without the certification perform like A1-rated cards. For example, The Wirecutter and Jeff Geerling published data showing that Samsung’s EVO+ cards had performance almost equal to the SanDisk Extreme Pro.

It’s uncommon because only two SanDisk cards are A1 rated. And that’s likely because the organization which governs the SD Card standard charges money in exchange for a rating. In reality, many other cards meet the criteria of the A1 certification.

2. Format and Configure Your microSD Card

Devices running an Android version below 6.0 Marshmallow require no further steps than partitioning the microSD card, which the system does for you. Android 6.0 and newer include special integration with the microSD card, which makes moving all the apps and data easy.

Formatting Your microSD Card

After getting a microSD card, you have to format it. Fortunately, after inserting a microSD card into an Android handset, the system automatically offers to format your storage. It’s simple.

However, Android does not automatically move apps to the card. To make a microSD card your primary space for holding apps, navigate to Settings > Storage. Then select your internal SD card as the Default write disk.

If the card is unformatted, you’ll need to do so manually. First, from the Storage settings menu, choose your external card by tapping on it. Once selected, tap on the three dots in the upper-right side of the screen. From the context menu, choose Format as internal (forgive the screenshot, my storage is already formatted as internal).

You can also choose to Migrate data from your internal storage to the microSD card. If you choose this option, the operating system will begin copying apps from your internal storage to the card. Note, though, that it will not copy system apps or apps with administrator privileges.

3. Partition Your microSD Card

On top of the issues with differing card sizes and speeds, even the latest versions of Android don’t properly use microSD cards. Fortunately, it’s possible to partition (separate) a microSD card into internal and external storage.

Doing so resolves the issue with being unable to transfer data (like media files) to and from the card. It also allows Android to encrypt sensitive portions of the card, making it unreadable to malicious third parties.

Formatting Your microSD Card as Internal and Removable

Thanks to XDA Senior Member Octanium91, you can now format a microSD card as both internal and external. This is particularly useful for those using custom ROMs, those moving media files between their computer and their microSD card, and, well, pretty much everyone. While this method works great, it, unfortunately, comes with some requirements.

Third, on a Windows computer, run aftiss.cmd from the downloaded files. Note that Linux users instead use aftiss.sh instead of the CMD file.

Fourth, choose one of four formatting modes. Be aware that each comes with its own advantages and disadvantages. My personal recommendation is to set the card at 25% SDCard and 75% Internal. It allows you a small amount of space for moving internal files around and a large amount of space for apps. Most media hoarders will probably be fine with keeping the card entirely as SDCard storage (portable storage).

After finishing the format, you can move the card to a computer and transfer files to the SDCard partition.

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armakuni

October 10, 2017 at 5:43 pm

Very nice article.

Personally, i recommend to integrate a microSD card at the very beginning of the usage in your phone. At the point where you change the default storage, the internal storage and the microsd simply get switched.

Get a very good card. Using a cheap one is a higher risk. If the card gets corrupt, Android remounts it readonly, but mostly silent. Only apps trying to write on the card will probably report the fault, but it's very likely to lose data (like at Whatsapp).

Personally I'm wondering about your step 3. It would be very interesting to find out how Android will react on a corrupt card.

I've never been able to recover a corrupt card. It always requires a reformat. And without an easy way to make a backup of a microSD card, it does sound risky. Those TLC cards, in my experience, are more prone to corruption than MLC cards.

Fortunately, from what I can tell, the repartitioning process of the microSD card is a simple script. It doesn't do anything special that the computer wouldn't do if you wanted to repartition the SD card using a gparted livedisk.

Based on my experiences with Samsung's RMA contractor in New Jersey, if you have a Samsung memory product fail, 7 out of 10 times you won't be getting a replacement. Sometimes Samsung doesn't even give you the correct address for returns, so I can't even say that it's entirely the contractor's fault. This is not a company to reward with business.

I prefer Intel for SSDs and SanDisk Extreme or Verbatim ProPlus for SD cards, having learned my lesson about Samsung memory products from both a reliability and service standpoint.

A couple huge down sides to using an SD card as internal storage: SD cards fail. They just do. They're not indestructible (see above). Also, a device with removable internal storage such as an adopted SD card REALLY can't have that card removed. The device will probably act funny unless everything is moved off of it prior to its removal or it is factory reset after the card is taken out. I'd rather use cards for bulk data than storing applications for this reason. At least I can easily pull the card and copy the data elsewhere when I'd like.

Android has also become increasingly poorly behaved with regard to SD card access. Many applications can't easily get access to the contents of arbitrary folders on the card or else they have restrictions for what they can and can't do with the contents of those external folders. For these reasons, I really think that use of an SD card should be limited entirely to bulk storage of media.

But hey, at least Android still understand the concept of extra disk drives, unlike the losers over in fruit-land, who as of iOS 11 just finally got official support for file browsing.

The Samsung RMAs (on smartphones) that I've done included ship-in costs -- which is lavish by the penny-pinching standards of modern RMA policies. But I live on the West Coast. I would bet that in smaller markets they use third party contractors (it's just more cost efficient that way) who probably aren't very good and more than likely try to deny ever RMA that comes in to save on workload.

I have four test units with microSD cards inserted (Android versions 4.0 through 7.1) and all of them are performing adequately. One of them bootlooped the other day and had to be hard reset -- and because the app directory is encrypted (with no way to turn it off) all the data was lost. There's no way to back it up, either.

Regarding reliability, you are absolutely right. My SD cards seem to fail if I even look at them the wrong way. I have a Dash Cam where the microSD card randomly stops recording every day or two and requires reformatting.

Really wish Kindles had the option to "format as internal" when it comes to apps and such. So many things get placed into on-board memory that would be so much nicer to have on the storage card. When you have a low-storage device in the first place, that doesn't help.

Whoa, that is really awful. I guess that's because FireOS is still based on Android 5, which lacks full microSD card support. You can still move apps to it IIRC, but only on a per-app basis. Many apps only support exporting user data to the card.

Kannon is a Tech Journalist (BA) with a background in international affairs (MA) with an emphasis on economic development and international trade. His passions are in China-sourced gadgets, information technologies (like RSS), and productivity tips and tricks.